In our study, we found that ultrasonographic evidence of a dark halo (in particular a halo of 1 mm) around the lumen of the temporal arteries had good specificity (93%), but low sensitivity (40%). In other words, the presence of halo ruled in a diagnosis of giant-cell arteritis but its absence did not exclude it. Schmid and colleagues (1) recently found that the halo sign had a sensitivity of 50% and a specificity of 100% for diagnosing giant-cell arteritis. As in our study, all of their patients were prospectively examined, had temporal artery biopsy, and underwent ultrasonography before the biopsy was performed. Ultrasonography, although specific, misses about half of the cases of giant-cell arteritis and cannot replace temporal artery biopsy in clinical practice. Temporal artery biopsy remains the gold standard for diagnosis of giant-cell arteritis.